Medical accelerators are used for radiation treatment of cancer patients and emit radiation in 360°. A patient lies on a platform, while a head of the device is rotated around the body of the patient. Quality assurance (QA) of the integrity of the medical accelerators is paramount to ensure the safe delivery of radiation treatment. The two main criteria used for QA is radiation reproducibility and mechanical integrity of the machine. The QA tasks specifically consist of quantifying the accuracy and precision of mechanical motions of the accelerators, various optical indicators, and the delivered dosimetry. FIG. 1 illustrates a chart of QA tasks per medical accelerator that must be performed daily, monthly, and annually.
FIG. 2 illustrates a front view of a medical accelerator used for radiation treatment. As illustrated in FIG. 2, one task of QA is to ensure that radiation beams along an axis and the positioning aids, in the form of laser beams, align at an isocenter of the medical accelerator. QA of this alignment is important in order to verify that the radiation beams along axis 1 are configured to treat the patient accurately without causing burns or other undesired side effects.
At present, almost all of the QA tasks listed in FIG. 1 are performed with different apparatus. The mechanical and optical components are examined visually, where the data is not amenable to documentation. For example, a technician checks the light source by directing the source onto the patient couch, and rotating it to make sure it moves about the isocenter of the medical accelerator. The dosimetry is measured with a variety of ionization detectors with the two-dimensional array of discrete detectors being most popular. Higher resolution measurements are measured with films where the data conversion process can be tedious. Some of these tasks are performed on a daily, monthly or yearly basis, and can take hours to perform. For example, while daily maintenance only takes approximately 10 minutes, a monthly maintenance of such machines to test the output and the mechanical integrity of the machine typically will take between 5-6 hours, the results of the testing partially documented. In fact, annual maintenance on the machine can take approximately 4 days to complete.
Currently, to assess integrity of collimator rotation, a piece of film is placed flat on the couch at the plane of the isocenter. A long slit beam of narrow width is set up, such as a slit of approximately 0.1 to 1 cm×20 cm. The piece of film is exposed with the collimator rotated at different angles. Alternately, with the collimator fixed, the table can be rotated at different angles. The film is developed after several different angles are shot to determine, visually or digitally, the dimension of the circle that encompasses all of the intersections of horizontal rays. This gives a measure of the isocenter integrity of collimator rotation. The resultant film is often referred to as a star-shot image.
The current method to assess the integrity of gantry rotation includes sandwiching a vertical film between two blocks of plastic. The sandwich of blocks and film is placed vertically in the plane of gantry rotation. A long slit beam is set up with the narrow width orthogonal to the vertical film. The gantry is rotated 360° around the vertical film block exposing the film at different gantry angles. After several different angles are shot, the film is developed. The dimension of the circle that encompasses all of the intersections of the vertical rays is determined either visually or digitally. This gives a measure of the isocenter integrity of gantry rotation.
Accordingly, there is a need in the art for a device that provides a faster and more accurate measurement of collimator rotation and gantry rotation.